ESTABLISHMENT AND GROWTH OF ANNUAL AND PERENNIAL GRASSES ON COPPER MINE TAILING SLOPES (ARIZONA).

Abstract

Research was conducted at Cyprus Pima Mine, an open pit copper mine located southwest of Tucson, Arizona, in 1980 and 1981 to study the establishment of annual and perennial grasses on the slopes of copper mine tailing ponds. In 1980, the north and south slope exposures were hydroseeded with barley (Hordeum vulgare L.). Plots were capped with topsoil prior to planting or left uncapped, and mulched with wheat straw after planting or left unmulched. Desert soil was classified as Palos Verdes-Sonoita Complex and Detrital-Sonoita Complex. Barley provided a quick, temporary cover and served as a mulch for later plantings. The number of seedlings established was the same for both exposures. Barley grew taller on the north slope possibly due to cooler temperatures. Barley growth was more vigorous on mulched areas. In 1981, the same north and south slopes were hydroseeded with Lehmann lovegrass (Eragrostis lehmanniana Nees.), buffel grass (Pennisetum cilare (L.) Link), blue panicgrass (Panicum antidotale Retz.) and bermudagrass (Cynodon dactylon (L.) Pers.). Prior to planting perennials, barley residue was incorporated into the slopes using a spike-tooth chain drag and a sheepfoot roller, or was left unincorporated. Incorporation of barley residue aided in its breakdown and helped prepare a good seedbed. The spike-tooth chain drag produced better growth than the sheepfoot roller, possibly due to excessive soil compaction with the sheepfoot roller. Capping tailing slopes with desert soil produced the most significant improvements in barley and perennial grass growth. Soil analyses of pure tailing and capped tailing revealed both were low in nitrogen and phosphorus. All plots were amended with these nutrients. Organic matter, although low for both samples, was higher in the capped tailing sample. Organic matter improves soil structure and provides nutrients and its increased presence may have been the main reason for improved growth on capped slopes.